Why does running feel harder in hot weather?

Understand why running can feel different in warm summer weather

If you struggle to run as far (or as fast) in hot weather, read our guide to hot weather running. Once you know what happens to your body when you run in hot weather, you can form the best stray for staying cool and hydrated.

Why do we get hot when we run?

When we run, we get hotter because our body is being more active: heart rate increases, muscles work hard, and metabolic processes all increase.

How does the body try to stay cool?

Our body tries to regulate itself by sending more blood than usual to the surface of the skin in order to cool the blood.

During the process of regulating internal temperature, we also start to sweat. But it’s not the act of sweating that cools us down – it’s actually when sweat evaporates on our skin.

Running in heat and humidity

It’s not just the heat that can cause a problem to runners – think about humidity levels, too.

High humidity means the air contains more water. This naturally means it will be more difficult to cool off through sweating, because the sweat can’t evaporate as effectively in humid air.

Running in humid weather presents other challenges. Because more blood is being directed to the skin (to cool you down), less oxygenated blood can get to the working muscles. This means your heart will beat hard and you might feel more out of breath. It’s just your body working extra hard to do everything you’re asking of it! But don’t be surprised if your “easy” pace suddenly feels a lot harder.

Sweating and hydration

Did you know there are actually two types of sweat? Eccrine sweat comes from the eccrine sweat glands which are all over the body. This kind of sweat is mostly water (98%-99%) plus some sodium chloride and other minerals, fatty acids, lactic acid, citric acid, ascorbic acid, and urea. The other kind f sweat (apocrine sweat) is secreted from sweat glands in our armpits, genitals, navel and nipples and tends to be smellier. Eccrine sweat doesn’t tend to smell at all – its main job is to cool us down.

It’s important to know that sweating affects blood volume and electrolyte levels, which is why hydration is more important in hot weather. You lose fluid, salts, minerals, and electrolytes when you sweat so you should use a sports drink or electrolyte mix (or dissolvable tabs).